For a given food intake, fat and energy metabolism in adipose tissue and muscle adapt to nutrient intakes. This adaptation to nutrition may be impaired in susceptible individuals or in obese patients by promoting weight gain, either in constitutional thinness (MC) by blocking it. The MC is a little known entity. These patients wish to grow for her and others. Can they? We have demonstrated abnormalities of hormones regulating appetite (ghrelin, PYY, GLP1 and leptin) that may participate in thinness. Furthermore, this thinness is associated with osteoporosis in 25% of true MC who is 25 years old.